Deprotection by Base-Catalyzed Hydrolysis

Base-catalyzed hydrolysis is employed primarily for the liberation of carboxyl groups protected as esters. The reaction involves direct attack by the hydroxide anion 

FIGURE 3.8 Deprotection of carboxyl groups by acid-catalyzed hydrolysis (A) of amides and (B) of esters. Protonation generates a relatively stable carbenium ion that usually requires heat to fragment it. 

FIGURE 3.9 Deprotection of carboxyl groups by base-catalyzed hydrolysis of (A) esters and (C) trifluoroacetamides, involving direct attack by the hydroxide anion. (B) tert-Butyl esters are resistant to saponification. 

A Neuberger. Stereochemistry of amino acids. Adv Prot Chem 4, 297, 1948. 

FIGURE 3.10 Deprotection of functional groups by beta-elimination.17 (A) Removal of a labile proton beta to a good leaving group leads to release of the protector as the didehydro compound. (B) Recently developed protectors (Samukov et al., 1988) also designated untra-ditionally as 4-nitrophenyl- (C) Transformation of an O-protected serine residue into a dehydroalanine residue by hefa-elimination. 

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